Section of the THOR survey in the region 39° < ℓ < 52°. The background image is a false-color representation of Midcourse Space Experiment 8 μm, WISE 4.6 μm, 12 μm, 22 μm, and THOR + VGPS radio continuum. H II regions appear as pink or bright yellow nebulae, while supernova remnants appear as blue nebulae. Symbols indicate RM (+ for THOR extragalactic sources and × for pulsars) with size proportional to ﹩| \mathrm{RM}| ﹩ up to 4219 rad m⁻², with red indicating positive and cyan indicating negative RM. Pulsar DMs are indicated by white squares, scaled proportional to DM, with the largest squares indicating DM ≈ 650 pc cm⁻³ (see Figure 3). The THOR latitude range is within the 1.8 kpc scale height of the WIM (Gaensler et al. 2008) at any distance within the Milky Way.